How long could life continue without the sun?

18 November 2007


If the sun were to blink out one day, how long do you estimate life could be sustained on Earth?


That's an excellent question and I think the answer will surprise you because I would be willing to put money on it being millions, if not billions of years. The reason I say that is because there was an answer to this question, sort of, provided not far away from where I am in South Africa - In a goldmine not far away from Johannesburg. About a year ago, Lisa Pratt who's a researcher in the US published a paper in the journal Science where she and her team had isolated some bacteria from 3km underground down a mine shaft. Water that was accompanying these bacteria, coming out of a hole from the side of this mineshaft was analysed and found to be between 16 and 40 million years old. In other words that water had been cut off from the rest of the Earth for up to 40 million years. When they cultured it, it was thriving with bacteria. So those bacteria themselves must also have been cut off from the rest of the world. So what were they eating in water, 3km underground in temperatures of 70 degrees centigrade? Analysis of how these bacteria survived suggests that what they're actually doing is living off radiation which is coming out of the rocks. There's a lot of uranium in the rock. Uranium spits out alpha particles, it has a helium nucleus, the alpha particle is radioactive and hits water particles. When it hits the water molecule it breaks it up into what's called a hydroxyl radical. The hydroxyl radical can jump into the nearby iron pyrites (fool's gold) which is in the rock and it breaks up the iron and the sulphur (iron sulphide) and turns it into a form of sulphur that these bacteria can metabolise. As a result these bacteria can grow and then feed other bacteria which are also present in there. My guess is that if the Sun suddenly went out, although all life that's dependent on the Sun would cease to exist or would probably die pretty fast, there would certainly be bacteria like these that can survive on other sources of energy such as radiation or those that survive around hydrothermal vents at the bottom of the sea.

I think we'd probably be stuffed. One little comfort is that, in fact, the light that's coming out of the Sun is already at least one million years old by the time it gets to us because it's been bounced around like a pinball inside the Sun before it escapes. Even if the Sun's nuclear reactor went off, for some reason, tomorrow you'd still have a million years' worth of light stored up inside.

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